Review on thermal energy storage with phase change: materials, heat transfer analysis and applications

Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

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Light-emitting diodes

Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

A review of Ga2O3 materials, processing, and devices

International Technology Roadmap for Semiconductors 2003の要求清浄度について － シリコンウエハ表面と雰囲気環境に要求される清浄度, 分析方法の現状について －

Small, light weight and multifunctional electronic components are attracting much attention because of the rapid growth of the wireless communication systems and microwave products in the consumer electronic market. The component manufacturers are thus forced to search for new advanced integration, packaging and interconnection technologies. One solution is the low temperature cofired ceramic (LTCC) technology enabling fabrication of three-dimensional ceramic modules with low dielectric loss and embedded silver electrodes. During the past 15 years, a large number of new dielectric LTCCs for high frequency applications have been developed. About 1000 papers were published and ∼500 patents were filed in the area of LTCC and related technologies. However, the data of these several very useful materials are scattered. The main purpose of this review is to bring the data and science of these materials together, which will be of immense help to researchers and technologists all over the world. The comme...

Low loss dielectric materials for LTCC applications: a review

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Cooling the Electronic Brain

Life prediction of LED-based recess downlight cooled by synthetic jet

The present work uses finite element thermal simulations of Gallium Nitride High Electron Mobility Transistors (GaN HEMTs) to evaluate the impact of device design parameters on the junction temperature. In particular the effects of substrate thickness, substrate thermal conductivity, GaN thickness, and GaN-to-substrate thermal boundary resistance (TBR) on device temperature rise are quantified. In all cases examined, the TBR was a dominant factor in overall device temperature rise. It is shown that a TBR increase can offset any benefits offered through a more conductive substrate and that there exists a substrate thickness independent of TBR which results in a minimum junction temperature. Additionally, the decrease of GaN thickness only provides a thermal benefit at small TBRs. For TBRs on the order of 10 -4 cm 2 K/W or greater, decreasing the GaN thickness can actually increase the temperature as the heat from the highly localized source is not sufficiently spread out before crossing the GaN-substrate boundary. The tradeoff between GaN heat spreading, substrate heat spreading, and temperature rise across the TBR results in a GaN thickness with minimum total temperature rise. For the TBR values of

THE IMPACT OF GaN/SUBSTRATE THERMAL BOUNDARY RESISTANCE ON A HEMT DEVICE

The compression process necessary for the liquefaction of natural gas on offshore platforms generates large amounts of heat, usually dissipated via sea water cooled plate heat exchangers. To date, the corrosive nature of sea water has mandated the use of metals, such as titanium, as heat exchanger materials, which are costly in terms of life cycle energy expenditure. This study investigates the potential of a commercially available, thermally conductive polymer material, filled with carbon fibers to enhance thermal conductivity by an order of magnitude or more. The thermofluid characteristics of a prototype polymer seawater-methane heat exchanger that could be used in the liquefaction of natural gas on offshore platforms are evaluated based on the total coefficient of performance (COP T ), which incorporates the energy required to manufacture a heat exchanger along with the pumping power expended over the lifetime of the heat exchanger, and compared with those of conventional heat exchangers made of metallic materials. The heat exchanger fabricated from a low energy, low thermal conductivity polymer is found to perform as well as, or better than, exchangers fabricated from conventional materials, over its full lifecycle. The analysis suggests that a COP T nearly double that of aluminum, and more than ten times that of titanium, could be achieved. Of the total lifetime energy use, 70% occurs in manufacturing for a thermally enhanced polymer heat exchanger compared with 97% and 85% for titanium and aluminum heat exchanges, respectively. The study demonstrates the potential of thermally enhanced polymer heat exchangers over conventional ones in terms of thermal performance and life cycle energy expenditure.

Energy Efficient Polymers for Gas-Liquid Heat Exchangers

Studies using commercial computational fluid dynamics software, running on a supercomputer, were carried out to investigate the effects of fin density, inlet duct velocity, and clearance area ratio, on the extent of flowbypass and its impact on the thermal performance of the heat sink. Flow bypass was found to increase with increasing fin density and clearance, while remaining relatively insensitive to inlet duct velocity. An optimum geometry, for a fixed inlet duct velocity, bypass clearance, fixed heat sink volume, and constant thickness, was determined.

Avram Bar-Cohen

Papers

Cooling the Electronic Brain

Life prediction of LED-based recess downlight cooled by synthetic jet

THE IMPACT OF GaN/SUBSTRATE THERMAL BOUNDARY RESISTANCE ON A HEMT DEVICE

Energy Efficient Polymers for Gas-Liquid Heat Exchangers

Bypass effect in high performance heat sinks